1. Field of the Invention
This invention relates to semiconductor circuit thermal management More specifically, it relates to on-chip liquid cooling of semiconductor devices.
2. Background
Thermal management is of great importance to the operation of semiconductor devices. Thermal management is especially important in the operation of silicon microprocessors as relentlessly increasing frequency targets push power (heat generation) output to the limits of the cooling capacity of passive air-cooled heat sink technology. Thermal management includes the art of dissipating the heat generated by a semiconductor device away from the device and allowing it to dissipate to the surroundings. Insufficient transfer of heat away from a semiconductor device can result in a degradation in the performance and reliability of that device or circuit. Typical thermal management solutions are to use low-cost aluminum or copper heat sinks to keep a semiconductor device cool.
Thermal management is especially critical in the packaging of highly integrated circuits. Very large scale integration and ultra-large scale integration circuits are currently generating up to 50 watts of heat that is required to be transported away from the integrated circuit to permit the circuit to function effectively. Current generations of integrated circuits are placing pressure on the ability of passive air-cooled heat sink technology to dissipate sufficient energy to allow the integrated circuit to function properly. Future generations of integrated circuits will clearly exceed the ability of current passive air-cooled heat sink technology to effectively manage the thermal environment of the integrated circuit.
A related problem is the increase of within die temperature gradients. Functional blocks of integrated circuits, such as a floating point unit, are much more active than other elements, for example the cache and therefore, heat up significantly more than these other elements. Temperature gradients within an integrated circuit of tens of degrees Celsius are now typical. This situation is likely to get worse. Since maximum device speed inevitably decreases as temperature increases, controlling temperature both on an overall device scale and on a local hot-spot scale is a key enabling technology for the production of future microprocessors.